1. Field of the Invention
The present invention relates to a three-dimensional shape measuring device for measuring a three-dimensional shape of an object to be measured (hereinafter, called as a “measurement object”) using a light section method, and a portable measuring device incorporated with the three-dimensional shape measuring device.
2. Description of the Related Art
There are known instruments such as a caliper and a micrometer for measuring the length of a measurement object while being hand-held by the user. These instruments are superior in operability because the user can manipulate the instrument while holding the instrument with his or her hand. The instruments, however, fundamentally need contact with the measurement object for measurement. There is also known a device for non-contactly measuring the length of a measurement object using an optical method. For instance, Japanese Unexamined Patent Publication No. Hei 8-233520 (D1) discloses a three-dimensional shape measuring device using a light section method. Currently marketed three-dimensional shape measuring devices, however, are generally large in size, and most of the devices are fixedly installed.
For instance, for dental treatment, accurate measurement of the shape of a tooth is required to form a tooth crown. In non-contactly measuring the shape of a tooth, users will find it convenient, if the measuring device is so designed as to be operable like a caliper or a micrometer. U.S. Pat. No. 6,480,287 (D2) discloses a handy three-dimensional shape measuring device using a light section method in order to satisfy the demand.
The three-dimensional shape measuring device using a light section method is operative to convert light such as a laser beam emitted from a point light source into a fan-shaped slit beam to irradiate a measurement object. It is required to project the slit beam onto the measurement object in a state that the slit length of the slit beam is sufficiently long to cover a measurement field. In a light projecting optical system covering from the point light source to the measurement object, a certain optical path length is required to secure a certain slit length.
In the three-dimensional shape measuring device disclosed in D2, a light projecting optical system including a light source is disposed on the measurement object side, and a light receiving optical system is disposed on the back side of the measurement object. In this optical arrangement, if miniaturization of the three-dimensional shape measuring device is attempted to realize a handy operation like a caliper or a micrometer, it is difficult to secure an optical path length capable of sufficiently extending the slit length. The slit length may be extended by a relatively short optical path length, if a lens having a strong optical power is disposed in the light projecting optical system. However, this may cause a distortion in a slit image, or make the lens designing infeasible or less feasible.